Homology-dependent Suppression of Stigma Phenotype by an Antisense S-locus Glycoprotein (SLG) Gene in Brassica rapa L.

Abstract

Self-incompatibility (SI) in Brassicaceae is sporophytically controlled by haplotypes of the polymorphic S locus complex. Two tightly linked polymorphic genes at the S locus, S-locus glycoprotein (SLG) and S-receptor kinase (SRK) genes, are specifically expressed in the stigma. S-haplotypes have been classified into class I and class II types based on the sequence similarity of their SLGs, and their SRKs. To investigate the effect of an antisense SLG gene on the class divergency of the endogenous SLG and SRK genes, we introduced an antisense class I SLG43 cDNA into a cultivar Osome in Brassica rapa which was heterozygous for class I S52 haplotype and class II S60. SLG43 is more similar to the endogenous SLG52 (87.8% identity) than to SLG60 (74.8% identity), Out of ten primary transformants analyzed, two were completely self-compatible; the SI phenotype of stigma was altered from S52S60 to S60, but that of pollen was not. In these two plants, the expression levels of mRNA and protein of SLG52 were reduced, whereas those of SLG60 were not. We suggest that an antisense class I SLG-transgene causes homology-dependent suppression, which leads to breakdown of the class I S-haplotype specificity in stigma but not the class II S-haplotype.